Design and calibration of a new surface-obstacle skin-friction and flow direction meter

Calibration data of surface-obstacle skin friction meters, including blocks, fences, Preston tubes and Stanton tubes, are examined throughout the available ranges of dimensionless wall-shear-stress and pressure-differential parameters. The calibration relationships, including the effect of compressibility, are reformulated in terms of variables containing physical quantities at the wall and including the probe size in only one parameter. In view of the current trend toward miniaturization, special attention was given to the range where the flow disturbance introduced by the probe remains within the near-linear part of the velocity profile. Criteria are derived for the smallest probe protrusion which provides a practically measurable differential pressure at given flow situation. Design of an adjustable/retractable surface-obstacle device for the Wright Laboratory M3 and M6 supersonic wind tunnels is described, and initial results obtained with a simple prototype in the Washington University low-speed wind tunnel are presented.